What are Lateral Marks?

A vessel does not always sail in open seas. Often, they ply in narrower water bodies like rivers, channels or canals, shallower water regions close to the shore while approaching a port or a harbour for docking, and encounter deltas and estuaries. In other words, a very critical aspect of navigation involves restricted conditions where the vessel needs to adhere to certain constraints

Lateral Marks

These constraints mean that a seafarer or navigator is not entirely free to navigate the vessel on his own accord, as many areas may be unnavigable and prohibited.

Flagging such zones as unnavigable may stem from a host of reasons: 

  • Due to the vicinity to the shore, the bathymetric conditions (hence, the low drafts available) are not congenial for a vessel to ply safely, as shallow depths pose a great risk of grounding and underwater hull damage. 
  • Submerged geography and topological restrictions are not favourable for sailing.
  • Hydrodynamic problems like unfavourable wave-breaking and tidal behaviour, bad current patterns, whirlpools, streams, etc. that are not conducive for vessels. 
  • Traffic from other vessels (such as near a port or harbour). 
  • Presence of structures like bridges, dams, submerged cables, offshore wind farms, etc. along the prohibited route. 
  • Ecological limitations like natural habitats and environmentally sensitive areas need to be avoided.  
  • Regions close to human habitations or communities; parts of the water body used for fishing and aquaculture
  • The presence of economic, commercial, defence, governmental, or any other facility on or close to the shore that needs a certain margin of the surrounding water zone to be kept restricted. 
  • Any other potential danger or hazard in certain marked areas that need to be kept off bounds. 

Lateral Marks 

Hence, when a seagoing vessel enters a restricted water body, and vice-versa, it must mostly follow a certain designated route. For the same purpose, the system of lateral marks acts as an aid to marine pilotage, helping identify the set boundaries a vessel needs to be within, without deviating.

These are remote, like the signage and indicators that help drivers identify the nature of the traffic flow on a busy road or the lights and unique system of markings on a runway or taxiway guiding an aircraft. 

The system of lateral marks is fixed for a particular region, except rarely on occasions when the designated routes for vessels are updated for some reason. The lateral marks at a specific region follow a particular pattern that a seafarer or a navigator needs to be well versed in. 

Not only do these lateral marks indicate the limits of a navigable path but also act as a trail that leads the vessel towards its destination in the given direction. When a vessel enters a restricted body of water from a sea or ocean and intends to travel further inside, this direction is known as the conventional direction of buoyage. This is also mostly the upstream direction. 

The lateral marks in a particular region are specific to the side of the vessel, that is for port, the signage is different from the one designated for the starboard. For any given vessel underway a certain route within restricted limits, the port side markers indicate that the vessel’s port side or by convention, the left side of the vessel when viewed along its forward surge direction, should be on the right side of them. Similarly, the starboard signage states that the vessel’s starboard side should be always on the left side of the markers (or the starboard signage should be right of the starboard side of the vessel). 

Now, the signage reverses when the vessel travels back from the restricted zones to the open waters, like from an inland channel back to the open seas. Since the direction of the vessel is now opposite to the original direction towards the restricted limits, that is upstream by convention, the markers which previously served as port signals now act as starboard indicators, and vice-versa. 

System of Markings 

How do we distinguish the port sides and starboard signs for any given route? The convention is decided by IALA and is specific to the region of application. 

These regions are divided into categories: 

  • Region A: Europe, Africa, Asia (except for Japan and South Korea), and southern countries like Australia. 
  • Region B: Americas, Japan, South Korea, Philippines, Taiwan, etc. 

For region A, all port side signage (the markers that need to be kept on the left side of the vessel) are red. They are of numerous shapes and forms, like cylindrical, spar-like, can-shaped, pillar-looking, and conical, and are often labelled with marks flashing consecutive odd numbers, like 1,3,5….

These marks may additionally have a cubical box-like projection at the tip. For night visibility, they are fitted with a top flashing redlight that can flash in any pattern other than the (2+1) rhythm, that is two quick flashes followed by a single flash. 

For starboard laterals that indicate that the vessel’s starboard side is to be kept left of the signage, similar marks but with green colour are followed. However, they follow a pattern of incremental even numbers, like 2,4,6….

They have green lighting following a similar pattern. Moreover, the top marks at the tip of the signage are pointed arrows, unlike the cubical shapes for the port. 

Navigation marks

Now often, there are situations when a waterway bifurcates, and the vessel needs to take a turn. This bifurcation is marked by a different marker indicating the cape or the tip of the dividing landmass, and the vessel needs to essentially veer off before that point towards a preferred direction. 

If the vessel needs to change its course to the path on the right, that is turn by starboard (known technically as preferred channel starboard), the marker is a striated green and red, with the green band at the centre. This marker should be on the port side of the vessel when it makes a turn by starboard towards the preferred channel or path on the right. The top light is a red one, like a normal port sign, following the same flashing pattern. 

Likewise, when the vessel needs to choose the path on the left, that is port, the signage is a similar striated mark but with the red band at the centre. This modified marker should be on the right or starboard of the vessel after it has taken the port turn. Hence, as for the rest of the features, it follows the same pattern as an ordinary starboard mark, that is having a pointed or arrow-like green shape at the top, and a green flashing light. 

For a vessel returning along the same route, the exact reverse order of the signage needs to be kept in mind by the seafarer or navigator. 

For regions under category B, the signage is completely the opposite. The marks on the port are green (odd-numbered) and the ones to be kept on the starboard side are red (even-numbered) when a vessel travels upstream from deeper waters to inner waterways. However, the shapes at the top (cubical for port and conical for starboard) are the same.  Accordingly, the port marks are characterized by a green flashing light, whereas the starboard ones are characterized by a red light. 

For junctions or intersections falling on the course of the vessel heading inland or upstream, the modified signage is also different. When a vessel needs to turn starboard now, that is keep the marker to its port, the striations of green and red colours have the latter band at the centre, unlike the Region A system (where markers had the green band at the centre). 

The flashlight is green. Similarly, for a vessel turning towards a channel or way on the port or left side (with its starboard facing the dividing marker), the green band appears at the centre. On the top, a flashing red light is fitted with the same pattern.

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About Author

Subhodeep is a Naval Architecture and Ocean Engineering graduate. Interested in the intricacies of marine structures and goal-based design aspects, he is dedicated to sharing and propagation of common technical knowledge within this sector, which, at this very moment, requires a turnabout to flourish back to its old glory.

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Disclaimer :
The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.


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